1. Technical Field
The present invention relates generally to a data receiving apparatus which may be employed in digital mobile communication, and more particularly to a data receiving apparatus designed to decode data at an appropriate signal identification point.
2. Background of Related Art
The data decoding in data receivers used in digital radio communication is usually accomplished by converting an input analog signal to digital signals and identifying logic levels of the digital signals at symbol identification points. The precise detection of the symbol identification points results in improved quality of a received signal.
FIG. 13 shows one example of such data receivers. The shown data receiver includes generally an in-phase signal A/D converter 3 and a quadrature-phase signal A/D converter 4, a demodulator 10, and a clock reproducing unit 12. The in-phase signal A/D converter 3 and the quadrature-phase signal A/D converter 4 sample an input signal 1 (i.e., an in-phase signal I) and an input signal 2 (i.e., a quadrature-phase signal Q), respectively. The clock reproducing unit 12 provides the A/D converters 3 and 4 with identification timing signals 13, each indicating the timing in which their sampling operations are to be performed. The demodulator 10 demodulates the signals sampled by the A/D converters 3 and 4 to provide demodulated data 11.
Narrow-band modulated signals usually need to be identified logically with timing where their eye patterns are opened most greatly for avoiding reduction in error rate. Thus, in the shown data receiver, the clock reproducing unit 12 determines timing where eye patterns are opened the widest to provide the identification timing signals 13 to the A/D converters 3 and 4, respectively, prior to demodulation in the demodulator 10. The A/D converters 3 and 4 are responsive to the identification timing signals 13 to sample the input signals 1 and 2, respectively. The demodulator 10 then demodulates the sampled signals. This prevents the bit error rate of the demodulated data 11 from being increased.
The above data receiver however has the drawback in that the demodulation operations cannot be performed until symbol identification information is derived, and a preamble signal needs to be added to a leading portion of data for reproducing clocks. This leads to reduction in data transmission efficiency.